1. Field of the Invention
The present invention concerns a hydromechanical power transmission device adapted to drive a driven shaft from a driving shaft at any rotation speed equal to, less than or greater than that of the driving shaft. Thus it may be thought of as a hydromechanical variable speed drive.
2. Description of the Prior Art
There are already known torque converters adapted to drive a driven shaft at the speed of a driving shaft, starting, for example, from a null speed (increasing speed function) using turbine blades attached to each of the two shafts and immersed in a transmission fluid. The efficiency of a hydraulic transmission device of this kind is very low because of losses associated with friction and with the viscosity of the transmission fluid employed. It is for this reason that, after the two shafts are synchronized, they are mechanically coupled in rotation with no further action by the hydraulic transmission: this necessitates a specific control device.
Apart from their low efficiency, currently known hydraulic torque transmission devices are relatively inflexible in use, there being in practice virtually no more than the basic provision for bringing a driven shaft up to the speed of a driving shaft.
An object of the invention is to alleviate these disadvantages by proposing a high-efficiency hydraulic device.
Another object of the invention is a torque transmission device adapted to drive a driven shaft over a wide range of speeds encompassing the possible speeds of the driving shaft and procuring great flexibility of utilization even in the case of driven shaft speeds of limited variation.